1. Field of the Invention
The present invention relates to a hydraulic damper, and more particularly to a hydraulic damper of the adjustable damping force type.
2. Prior Art
A typical well known hydraulic damper of the adjustable damping force type generally comprises a cylinder containing hydraulic liquid, a piston rod having a bore formed therein and extending axially thereof, with one end thereof inserted into the cylinder and with the other end thereof extending to the outside of the cylinder, a piston secured to the one end of the piston rod and partitioning the interior of the cylinder into two liquid chambers, a liquid passage allowing for communication between the two chambers through the bore in the piston rod, at least a pair of orifices disposed midway of the liquid passage, an adjusting rod rotatably inserted into the bore in the piston rod and being adapted to be rotatably operated from the side of the other end of the piston rod, and a shutter secured to one end of the adjusting rod and having a pair of openings radially formed therein for opening and closing both of the orifices.
However, in a hydraulic damper according to the prior art such as described hereinfore, each of the two orfices comprising a pair are located at positions which are diametrically opposed along the diametral line of the liquid passage. The openings formed in the shutter are also located at positions which are diametrically opposed along the diametral line of the shutter. Therefore, when the orifices are opened and closed through the openings in the shutter, each of the two orifices which comprise a pair begin to open and close substantially simultaneously, and as a result the damping force generated changes rapidly. Such rapid changes in the damping force very often cause unusual noises and vibration.